Cellulosic material



April 10, 1945. BlERWlRTH 2,373,374

' CELLULOSIC MATERIAL Original Filed Dec. 2'7, 1941 RED! 0 FREQUENCY C ILL 17 7'07? Enventor Rudolph Bier wirth (Ittorneg CELLULOSIC MASTER Rudolph A. Bierwirth, Kingston, N. 3., assignor to Radio Corporation of America, a corporation oi Delaware Original application December 27, 1941, Serial No. 424,670. Divided and this application March 9, 1943, serial No. 478,557

(Ci. BN1) 4 Claims.

This invention relates to the manufacture of materials from viscose or the like, and more particularly to an improved cellulosic product of this part of the cake. Thus, strains are set up in the ayers of thread on the outside of the cake. As

, the drying progresses, the layers of thread furtype and the method of forming the same, the

present application being a division of my co pending application, Serial No. 424,679, filed December 27. 1941.

In manufacturing artificial silk and similar artificial materials from viscose or the like, the cellulose is dissolved in a suitable solvent and the does or nozzles to form filaments of the desired shape from which threads, tape, or the like may be formed. These threads or tapes are treated with suitable precipitating chemicals after which they are stretched more or less to impart a gloss or luster thereto. The thread is then wound to form a self-=supporting spool or cake and placed in a cloth container, after which it is thoroughly washed in water to remove the precipitating chemicals employed in coagulating the viscose material,

In the wet condition, the thread is rather soft and distended or swollen due to the water contained therein and adhering thereto. The weight of the washed cakes, as they are known, is about three pounds, of which approximately two pounds is water and only one pound is rayon. To remove the water and to dry the cakes, it has been customary to place them in large drying rooms where heated air is circulated around them. The cakes must not be heated to a temperature in excess of 140 Fahrenheit or the quality of the rayon will be impaired. At temperatures in the neighborhood of 140 Fahrenheit, the cakes must be exposed to the drying air for about one hundred hours before they are suitably dried.

One of the characteristics of rayon thread is that it changes its physical dimensions with changing moisture content. If wet thread is dried, it shrinks and its length tends to decrease. If the thread is mechanically prevented from resulting solution is forced through shaping orilit shrinking while drying, a strain is set up therein ther inside of'the cake tend to shrink, and the point is reached after a time when the inner part of the cake will not be strong enough to prevent the shrinkage of the relatively outer layers and will collapse and buckle up. Consequently, part of the cake is strained and part is not, so that, when the thread is made up into cloth,'an irregularappearance results with part of the cloth having a higher luster than other parts thereof.

In my copending application, Serial No. 407,619, filed August 0, 1941, now Patent No. 2,325,652, I have disclosed a method of heating the cakes rapidly and uniformly by applying thereto a high frequency electric field while maintaining the cake under a partial vacuum. Since the heat is applied uniformly throughout the entire cake according to this method, the drying proceeds uniformly with the result that whatever shrinkage takes place occurs uniformly throughout the entire cake without setting up strains in the thread or causing buckling of the inside of the cake. Moreover, the cakes are subjected to a temperature well under 140 Fahrenheit for approximately an hour, as compared with a period of approximately one hundred hours at a temperature approaching 140 Fahrenheit required by previously practiced methods. As a consequence, cloth or fabric made from rayon dried in accordance with the method of my aforementioned patent is far superior to that dried by conventional air-drying methods.

Further investigation has disclosed that optimum results may be obtained by using a frequency of about 25 magacycles and a vacuum of about 29 inches of mercury in drying the cakes according to the improved method which is the subject matter of my present invention. This results in a drying time of approximately one hour with the temperature at from F. to F. during most ofthe drying cycle and rising to from about F. to about F. at the end of the drying cycle. I have discovered that the rayon dried in accordance with this improved method is uniformly free from strains along its entire length and therefore has a uniform appearance throughout, being uniformly light-reflective. Furthermore, the thread thus dried has a greater tensile strength than the thread dried according to the prior art practice. When woven into cloth, the resulting material is markedly free from the irregularities in appearance usually found in cloth woven from rayon thread which has been dried by the method of the prior art. I have further discovered that the rayon dried in accordance with my improved method can be dyed much more readily and much more uniformly than the gling and/or breaking of the thread. In contrast, the cakes dried by my improved method do not produce buckling and consequent kinking of the inner portion thereof, with the result that the annoying and time wasting breaks in the thread are eliminated.

The primary object of my present invention, then, is to provide an improved thread of rayon and the like which is free from the objectionable features found in rayon produced by the prior art methods.

More particularly, it is an object of my present invention to provide an improved rayon thread which has a uniform appearance throughout and which is uniformly free from strains.

Another object of my present invention is to provide an improved rayon fabric which is markedly free from glossy stripes or the like which contrast with the remainder of the fabric, as found in the priorart, and which is entirely devoid of shiners," or lengths of thread having 8! portions which possess a high gloss in contrast to the surrounding and relatively dull cloth.

A further object of my present invention is to provide an improved fabric of artificial silk or the like which is uniform in appearance throughout, and which has a uniform weave.

It is also an object of my present invention to provide an improved method of drying rayon cakes which is characterized by optimum drying conditions. a

The novel features that I consider characteristic of my invention are set forth with particuiarity in the appended claims. The invention itself, however, as well as additional objects and advantages thereof, will best be understood from the following description, when read in connection with the accompanying drawing, in which Figure 1 is a diagrammatic view of a. drying apparatus employing the method of my present invention,

Figure 2 is a section or length of thread formed according to the prior art,

Figure 3 is a fragment of a piece of fabric woven from thread such as that shown in Figure 2,

Figure 4 is a viewsimilar to Figure 2 but showing a length of thread formed in accordance with my present invention, and

Figure 5 is a fragment of a piece of fabric woven from my improved thread. 7

Referring more particularly to the drawing, there is shown, in Figure 1, a container I providing a chamber which may be suitably evacuated by a vacuum pump or the like 3 connected to a chamber 1 through a condenser 5. Within the chamber I are a pair of spaced and prefervided with a plurality of insulated legs l8 which rest on the floor of the container I.

The material to be dried, such as the "cake of rayon 20, is placed on the electrode 9 and the electrode 1 is placed on top of the cake whereby the cake is disposed between each of the electrodes I and 9. The vacuum pump 3 is preferably operated to produce a vacuum of not less than 29 inches of mercury in the container I; and radio frequency voltage of the order of megacycles per second is then applied to the electrodes I and 9 from the oscillator I I. The dielectric losses in the cake 20 serve to heat the cake and thereby evaporate or drive off the moisture therefrom, the heat being applied uniformly and concurrently to all portions or layers of the thread forming the cake 20. Thus,.every portion of the entire length of thread in the cake is dried at substantially the same time whereby the rela tively outer layers are prevented from being strained and buckling of the inner layers is avoided. The condenser 5 serves to condense the water vapor which is removed from. the cake 20.

I have found that, by applying a moderate amount of power to the cake (about 600 or 1,000 watts) at a frequency of about 25 megacycles and a vacuum of about 29 inches of mercury, complete drying of the cake may be effected in approximately one hour. In such case, the cake is subjected to atemperature of from about 90 F. to about 100 F. for approximately to minutes and to a temperature of from about 120 F. to about 130 F. for from 5 to 10 minutes thereafter.

In Figure 2, which represents a length of thread formed according to the drying methods of the prior art, the thread is characterized by a section or portion 2! which, being on the outside of the cake, has been placed under tension and 0 therefore has a relatively higher luster than the remaining portion 22 of the thread, as well as being of somewhat smaller cross section than the portion 22. The fabric represented in Figure 3 and made up of the warp threads 23 and the a weft threads 24 is formed by weaving the threads 50 tion 2|. Moreover, fabric woven by such thread 85 stretched portion 22.

is found to have an uneven weave, the interstices being non-uniform throughout the fabric by reason of the fact that the stretched portion 2| is of slightly smaller cross section than .the un- This combination of a shiny stripe and larger interstices through which light passes more easily and through which the background against which the fabric is placed may be more readily seen results in an uneven appearance of the fabric.

In Figure 4, there is shown a length of thread 25 formed in accordance with my present invention. It will be. noted that the thread is uniform in thickness and uniform in gloss throughout its entire length. The fabric 25 of Figure 5 which is woven from the thread 25 has a. uniform appearance throughout its entire length first because it is entirely devoid of shiny stripes, and secondly because the interstices therein are of uniform dimensions.

From the foregoing description, it will be apparent to those skilled in the art that I have provided an improved rayon and other similar thread which has many advantages over like threads heretofore produced, as well as a novel method of producing the same. I attribute the improved results to the rapid and uniform drying throughout the entire cake. The concurrent drying of all portions or layers of the thread avoids setting up uneven strains therein. Moreover, by not subjecting the rayon to prolonged drying at fairly high temperatures, as in the drying ovens of the prior art, the chemical change throughout the thread and resulting hardness thereof, particularly on the outer surface, which i believed to take place as a result of prolonged exposure to heat is avoided, and as a result the threads formed according to my present invention and the fabric woven therefrom are much more receptive to dyes than are the threads and fabrics of the prior art. This, of course, further helps to impart to the finished cloth a more uniform appearance.

Although I have shown and described but one method of carrying out my present invention, it will be obvious to those skilled in the art that other equivalent methods are possible I therefore do not wish to be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims. 4

I claim as my invention:

1. A thread of dry artificial silk resulting from the drying thereof by heat produced internally of said thread uniformly throughout its entire length and cross section.

out its entire mass by heat produced internally of said thread as a result of dielectric losses therein when subjected to the action of a high frequency electric field.

3. A cellulose thread of sufilcient length to produce a spool-like cake weighing in. the neighborhood of one pound when dry and having substantially uniform physical and optical properties throughout its entire length, said thread resulting from the uniform drying of said cake concurrently throughout its entire mass by heat developed therein by dielectric losses produced in said cake by a high frequency electric field in which said'cake is immersed.

4. A synthetic fiber thread resulting from the uniform heating thereof concurrently throughout its entire mass by heat produced internally of said thread as a result of dielectric losses therein when subjected to the action of a high frequency electric field.

RUDOLPH A. BIERWIRTH. 

